SQLite

  SEEK(0);
  SimulateIOError( got = -1 );
  if( got==amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    return SQLITE_IOERR_READ;
  }else{
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
** Seek to the offset in id->offset then read cnt bytes into pBuf.
** Return the number of bytes actually read.  Update the offset.

    got = -1;
  }
  if( got==(DWORD)amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    return SQLITE_IOERR_READ;
  }else{
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.279 2007/01/03 15:34:30 drh Exp $
** @(#) $Id: pager.c,v 1.280 2007/01/03 23:36:22 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

*/
static void pager_unlock(Pager *pPager){
  if( !MEMDB ){
    sqlite3OsUnlock(pPager->fd, NO_LOCK);
    pPager->dbSize = -1;
  }
  pPager->state = PAGER_UNLOCK;
  assert( pPager->pAll==0 );
}


/*
** Unlock the database and clear the in-memory cache.  This routine
** sets the state of the pager back to what it was when it was first
** opened.  Any outstanding pages are invalidated and subsequent attempts

  pPager->nPage = 0;
  pPager->aHash = 0;
  if( pPager->state>=PAGER_RESERVED ){
    sqlite3pager_rollback(pPager);
  }
  pager_unlock(pPager);
  pPager->nRef = 0;
  assert( pPager->journalOpen==0 );
  assert( pPager->errCode || (pPager->journalOpen==0 && pPager->stmtOpen==0) );
}

/*
** When this routine is called, the pager has the journal file open and
** a RESERVED or EXCLUSIVE lock on the database.  This routine releases
** the database lock and acquires a SHARED lock in its place.  The journal
** file is deleted and closed.

**
** This function always succeeds. If a transaction is active an attempt
** is made to roll it back. If an error occurs during the rollback 
** a hot journal may be left in the filesystem but no error is returned
** to the caller.
*/
int sqlite3pager_close(Pager *pPager){
  PgHdr *pPg, *pNext;
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
  /* A malloc() cannot fail in sqlite3ThreadData() as one or more calls to 
  ** malloc() must have already been made by this thread before it gets
  ** to this point. This means the ThreadData must have been allocated already
  ** so that ThreadData.nAlloc can be set.
  */
  ThreadData *pTsd = sqlite3ThreadData();
  assert( pPager );
  assert( pTsd && pTsd->nAlloc );
#endif

  switch( pPager->state ){
    case PAGER_RESERVED:
    case PAGER_SYNCED: 
    case PAGER_EXCLUSIVE: {
      /* We ignore any IO errors that occur during the rollback
      ** operation. So disable IO error simulation so that testing
      ** works more easily.
      */
      disable_simulated_io_errors();
      sqlite3pager_rollback(pPager);
      enable_simulated_io_errors();
  disable_simulated_io_errors();
  pager_reset(pPager);
  enable_simulated_io_errors();
      pager_unlock(pPager);
      assert( pPager->errCode || pPager->journalOpen==0 );
      break;
    }
    case PAGER_SHARED: {
      pager_unlock(pPager);
      break;
    }
    default: {
      /* Do nothing */
      break;
    }
  }
  for(pPg=pPager->pAll; pPg; pPg=pNext){
#ifndef NDEBUG
    if( MEMDB ){
      PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
      assert( !pPg->alwaysRollback );
      assert( !pHist->pOrig );
      assert( !pHist->pStmt );
    }
#endif
    pNext = pPg->pNextAll;
    sqliteFree(pPg);
  }
  TRACE2("CLOSE %d\n", PAGERID(pPager));
  assert( pPager->errCode || (pPager->journalOpen==0 && pPager->stmtOpen==0) );
  if( pPager->journalOpen ){
    sqlite3OsClose(&pPager->jfd);
  }
  sqliteFree(pPager->aInJournal);
  if( pPager->stmtOpen ){

    /* If this was a malloc() failure, then we will not be closing the pager
    ** file. So delete any journal file we may have just created. Otherwise,
    ** the system will get confused, we have a read-lock on the file and a
    ** mysterious journal has appeared in the filesystem.
    */
    sqlite3OsDelete(pPager->zJournal);
  }else{
    pager_unlock(pPager);
    pager_reset(pPager);
  }
  return rc;
}

/*
** Acquire a write-lock on the database.  The lock is removed when
** the any of the following happen: